The present invention relates to an antenna device in a form of printed or inlaid conductor in a surface of conduit and used for a wireless system which includes cordless apparatuses such as a home telephone system, a home automation system, a home bath system, or a factory automation system.
A home automation (HA) system is one of the systems of the kind described and now a popular installation in ordinary houses. An HA system may include telephone sets and fire alarms which are located in individual rooms of a house, an electric lock, and others which are commonly connected to a system controller by a distributing cable to be controlled thereby. The system controller is installed in one of the rooms and connected to a public telephone line. Connected to another public telephone line is a cordless telephone system which includes a central unit fixedly located in one of the rooms, and at least one mobile unit located in another room. A problem with such a cordless telephone system which is not directly connected to the system controller is that a communication between, for example, the mobile unit or cordless telephone and any of the telephones connected to the system controller must be done through the respective public telephone lines and their exchange. Further, while a communication is established between the central and mobile units of the cordless telephone system, the electromagnetic wave must propagate through the walls which intervene between the central and mobile units. This brings about the need for intense electromagnetic power outputs because those walls are usually made of materials which tend to attenuate or obstruct the propagation of electromagnetic waves.
In the light of the above, there has been proposed a system in which an antenna is installed in each room and connected to a distributing cable via an exclusive duplexer, the cable being connected to a system controller having a transmit/receive circuit. This implementation allows an electromagnetic wave to be directly propagated through the space without the interference of walls and others, whereby the distance of transmission and reception of an electromagnetic wave and, therefore, the intensity of electromagnetic wave required is cut down.
However, the prior art system described above has a drawback that installing duplexers one for each antenna requires complicated and, therefore, time- and labor-consuming work which adds to the cost.